Well, I hope not, I've had my pond in the ground for almost 17 years now, in
one form or another, and I have cats and dogs both, they drink from it on a
regular basis. None of them has ever taken ill from it.
There are plenty of other things in a garden that can make a pet ill. Toads
and Frogs both can.
Another problem is slug and snail bait, it can be lethal.
Your friend just wasted his time in my opinion......
Bear